How draw PCX image with transparency?

coder123

Hi,

I have some .pcx images with black background. And want to draw this images with the black transparent.

I could use al_convert_mask_to_alpha but the black color is not exactly (0,0,0) it could be (0,1,0) etc.

How set transparency to this black background of pcx images?

I using al_draw_bitmap_region() to draw bitmap. A5.

Thank you.

Trent Gamblin

al_convert_mask_to_alpha is the only thing Allegro offers to do this. I've found a Windows(tm) tool called Greenfish Icon Editor to be great for removing backgrounds though. It has a "Remove Matte" function which will turn the black to alpha... not guaranteed to work but for me it did.

LennyLen

I've attached a command line utility you can use to convert the near-black pixels in your images to black pixels. Press SPACE to increase the tolerance value it uses to replace pixels and S to save. ESC exits the program.

Each pass through, any pixels that are converted are made transparent on a copy of the image which is then drawn over a light blue background. This will allow you to still see any dark background pixels that haven't been converted to black yet.

Here's the code (Allegro 4):

#SelectExpand
   1#include <allegro.h>
   2#include <stdio.h>
   3
   4
   5int keyrel(int k)
   6{
   7    static int initialized = 0;
   8    static int keyp[KEY_MAX];
   9
  10    if(!initialized)
  11    {
  12        /* Set the keyp (key pressed) flags to false */
  13        int i;
  14        for(i = 0; i < KEY_MAX; i++) keyp[i] = 0;
  15        initialized = 1;
  16    }
  17
  18    /* Now for the checking
  19       Check if the key was pressed
  20    */
  21    if(key[k] && !keyp[k])
  22    {
  23        /* Set the flag and return */
  24        keyp[k] = 1;
  25        return 0;
  26    }
  27    else if(!key[k] && keyp[k])
  28    {
  29        /* The key was released */
  30        keyp[k] = 0;
  31        return 1;
  32    }
  33    /* Nothing happened? */
  34    return 0;
  35}
  36
  37
  38int main(int argc, char *argv[]) {
  39
  40    int x, y, color, hue;
  41
  42    if (argc < 2) {
  43
  44        printf("No .pcx file specified.");
  45        exit(1);
  46    }
  47
  48    allegro_init();
  49    install_keyboard();
  50    set_color_depth(desktop_color_depth());
  51    set_gfx_mode(GFX_AUTODETECT_WINDOWED, 640, 480, 0, 0);
  52
  53
  54    BITMAP *src = load_bitmap(argv[1], NULL);
  55    if(!src) {
  56
  57        allegro_message("Error loading %s", argv[1]);
  58        exit(1);
  59
  60    }
  61
  62    BITMAP *magic_src = create_bitmap(src->w, src->h);
  63    if(!magic_src) {
  64
  65        allegro_message("Error creating secondary bitmap");
  66        exit(1);
  67
  68    }
  69
  70    BITMAP *buffer = create_bitmap(SCREEN_W, SCREEN_H);
  71    if(!buffer) {
  72
  73        allegro_message("Error creating buffer");
  74        exit(1);
  75
  76    }
  77
  78    blit(src, magic_src, 0, 0, 0, 0, src->w, src->h);
  79
  80    for (y = 0; y < magic_src->h; y++) {
  81
  82        for (x = 0; x < magic_src->w; x++) {
  83
  84            color = getpixel(magic_src, x, y);
  85            if (color == makecol(0, 0, 0))
  86                putpixel(magic_src, x, y, makecol(255, 0, 255));
  87
  88        }
  89
  90    }
  91
  92    int done = 0;
  93    int tolerance = 2;
  94
  95    while (!done) {
  96
  97        if (key[KEY_ESC]) done = 1;
  98
  99        if (keyrel(KEY_SPACE)) {
 100
 101            for (y = 0; y < src->h; y++) {
 102
 103                for (x = 0; x < src->w; x++) {
 104
 105                    color = getpixel(src, x, y);
 106                    hue = getr(color) + getg(color) + getb(color);
 107
 108                    if (hue <= tolerance) {
 109
 110                        putpixel(src, x, y, makecol(0, 0, 0));
 111                        putpixel(magic_src, x, y, makecol(255, 0, 255));
 112
 113                    }
 114
 115                }
 116
 117            }
 118
 119            tolerance += 2;
 120
 121        }
 122
 123        if (keyrel(KEY_S))
 124            save_bitmap(argv[1], src, NULL);
 125
 126        clear_to_color(buffer, makecol(0, 255, 255));
 127        draw_sprite(buffer, magic_src, 0, 0);
 128        blit(buffer, screen, 0, 0, 0, 0, buffer->w, buffer->h);
 129
 130
 131    }
 132
 133    return 0;
 134
 135}
 136END_OF_MAIN()

coaxil

You could, dunno, batch-edit your pictures to replace black pixels with zero alpha.

Edgar Reynaldo

Just use Paint.net or Gimp to flood fill black with a high (20% tolerance) - that should give you a decent edge.

LennyLen

coaxil said:

You could, dunno, batch-edit your pictures to replace black pixels with zero alpha.

PCX doesn't support alpha.

coder123

I've implemented your code in my Draw function.
And it works.

Thank you.

LennyLen

Ok, but be sure too realize that it wasn't designed to be used during the running of the game itself, and it could slow your drawing down considerably.

The intended use is for you to go over all the graphics you do have and replace them so that you can use them in your game without having to modify them at runtime.

Thread #611849. Printed from Allegro.cc